Decimal Year Convention:

We follow the same decimal year convention used by JPL for GIPSY time series. The file linked below contains an unambiguous mapping of decimal year to date given in YYMMMDD (Y=year, M=month, D=day).
The decimal year can be used as a time argument for plotting, kinematic fitting, etc.
This year has exactly 365.25 days for all years.
The year is exactly an integer for leap years on January 1, 12:00 (noon) GPS time.
Therefore 00JAN01 = 2000.0000, 04JAN01 = 2004.0000, etc.

This file also contains values for other date conventions, including separate fields for the Modified Julian Day (mjday), GPS week (week), day of GPS week (d), and J2000 seconds (J2000_sec). This file can be useful for translating between different date values.

The file with a mapping from dates in YYMMMDD format to decimal year and other formats can be found by clicking
THIS LINK.